According to ABBREVIATIONFINDER.ORG, DC is called direct current to the current produced by generators that maintain in their terminals the same type of electricity (+), (-) so when they are connected in a circuit the current flows in the same sense.
Apparently the first scientific observation of electrical effects was made by Thales of Miletus in 600 BC. He saw the dry grass blades stick to a piece of amber when it had been rubbed off.
Thousands of years later, exactly in 1660, it was the English physician and physicist William Gilbert who studied these effects, and taking the Greek word elektron (amber), he called these substances electrical. Being an apparently stable effect, unless it was disturbed it ended up being called static electricity, or lacking movement.
William Gilbert had written a book on the subject of magnetism, it was in 1600 and it was called “De Magnete”. Also Thales had studied the phenomenon, but it would be some time before physicists realized that it was the same phenomenon. Both electricity and magnetism would go on to form electromagnetism. Meanwhile, an attempt was made to discover the secrets of this strange phenomenon, and to unravel the hidden mechanism behind the electricity.
In 1733 the Frenchman Charles-François de Cisternay Du Fay, discovered that two cork balls charged in the same way repelled each other. But if he charged each one by different means, he sometimes got them to attract each other; for example if he loaded one by rubbing it with a resin rod and the other with a glass rod. This phenomenon of attraction and repulsion seemed to indicate two different natures. François de Cisternay Du Fay believed that electricity was a fluid, and determined that it existed in two types: Resinous or vitreous (positive and negative).
In the year 1747 Benjamin Franklin proposed that there were not two types of fluids, but one, which could be present in excess or in defect. But he renamed the fluid “negative electricity” if it was lacking for equilibrium, and “positive electricity” for excess. These names persist to this day, but with a different understanding of the phenomenon than that of a fluid.
In 1780, Luigi Galvani, an Italian anatomist, observed for the first time that an electrical discharge on the legs of a dead frog produced contractions of the affected muscles. He tried exposing these muscles to the effects of a storm. To achieve this, he hung hooked frog legs on the fence of the house. But the contractions continued even after the storm had passed. Further inspection led him to see that the stimulation occurred when the muscle simultaneously touched two different metals.
Luigi Galvani believed that the electricity thus produced was generated in the muscle, an observation that turned out to be wrong, but he would not be the one to discover the error.
Twenty years later, in 1800, Alessandro G. Volta assumed the opposite, that is, it was the contact between dissimilar metals that generated electricity. This idea was the beginning of a great revolution on the subject. This hypothesis could be immediately verified and allowed him two great advances:
- Build the first electricity-generating chemical device, which he called an electric battery, today called a battery.
- Obtain a continuous and sufficiently stable current for the first time in history. No longer depended on static.
The first pile of Alessandro G. Volta was being perfected. In 1836 it was improved by the British John Daniell (1790 – 1845), who achieved greater stability and durability.
Before this, in 1820, there had been a great leap in understanding about the relationship between electricity and magnetism. In that year the Danish physicist Hans Christian Oersted showed that a current generated a magnetic field. Following this discovery, André-Marie Ampèreshowed that a solenoid (wire wound in the form of a spring) considerably increased the generated magnetic field, in direct proportion to the number of turns the wire was turned.
Thus, from the pile of Alessandro G. Volta, which allowed working with a current, the discoveries were unleashed quickly.
- 1821: (The year after Oersted’s discovery). Michael Faraday, another important man for science, contributed the fundamental idea of modern physics, for the first time to describe an electromagnetic force it was spoken of field.
- 1823: William Sturgeon, taking advantage of the effect of solenoids, invented the electromagnet. The first of them was able to lift a weight of 4 kg.
- 1827: George Simon Ohm defined electrical resistance and proposed the law that bears his name: Ohm’s Law.
- 1831: Michael Faraday develops the transformer and the electric generator. Joseph Henry creates the electric motor and develops an electromagnet that lifts a ton of iron.
- 1883: Nikola Tesla develops a motor that could work with alternating current and no longer with direct current. Tomas Alva Edison was against the use of that current, but his efforts were in vain.
The task of continuing to describe the advances so far in electricity or its subsequent technological applications would be monumental. But it would not be an exaggeration if it were said that the current civilization would return to a primitive state if there was no knowledge of this form of energy, because for this the passage of the pistol of Alessandro G. Volta, forerunner of the spark plugs, was needed.